THIS invention relates to a mattress inner spring assembly.
The term “mattress” is used broadly in this specification to refer to a resilient cushion for use as a bed mattress or as a cushion in other items of upholstered furniture, for example chairs or sofas.
The invention is specifically concerned with mattress inner spring assemblies which make use of open-ended coil springs such as so-called LFK springs. It is well known in the art that such springs have a tendency to incline or cant in a preferential direction when compressed. Such tendency is described in detail and is illustrated in U.S. Pat. No. 6,375,169 assigned to Hickory Springs Manufacturing Company. As explained with reference to FIG. 1 of this document, the inner spring assembly of the mattress will exhibit severe lateral instability if all the springs are of the same hand, i.e. their coils spiral in the same direction, and are similarly oriented.
With reference to FIG. 2, U.S. Pat. No. 6,375,169 also describes one prior attempt to overcome the problem of lateral instability by using alternating rows of springs with the springs in one row of opposite hand to the springs in the adjacent rows. With reference to FIGS. 7 and 9 the document describes other potential solutions to the lateral instability problem. In the proposal illustrated in FIG. 7, each row and each column of springs in the assembly is composed of springs which alternate between right hand and left hand. Like the proposal illustrated in FIG. 2, the use of springs of different hand may create problems in automatic assembly. The FIG. 9 proposal is a complicated one making use of springs which are all of the same hand but in which each row and each column is composed of springs of alternating orientation.
It is an object of the present invention to provide a somewhat simpler construction in which all springs are of the same hand.